Formal Methods in Software Engineering

Transcription

1 Formal Methods in Software Engineering Introduction to Atelier B Installation This section describes the Atelier B installation procedure. For Window operating system, installation is fully automatic.

2 Just follow the assistant to simply install Atelier B. It will ask you for some preferences, for instance: the installation directory.

3 Finally, if the installation is correct, it will display the following window:

4 Main GUI The main GUI looks like the following screenshot:

5 Editor Atelier B furnishes a special editor specially customized for B component edition. It proposes functionalities like: completion, error underlining, etc... It looks like this: Its main functionalities are: Component editing, PMM file associated to B component editing, RMF file associated to B component editing, Patch Prover and Patch Rafiner editing, Syntaxic coloration, Printing, Auto-completion and automatic indentation, Some syntax checking, Navigation between open files. It also includes a presentation of language B symbols with facility to insert them in a component.

6 To start a development with the Atelier B, you will have to: 1. Create a project The Attach project function allows all users to declare a new project in Atelier B. The information required to declare the project is: the name of the new project and its owner, the Project Database directory (PDB) used by Atelier B to store internal files, the translation directory used by Atelier B to store translated files. The project type (non required) : SOFTWARE for B-Software projects, SYSTEM for Event-B projects. By default, the newly created project is considered as software. To reference a given project, only the PDB and translation directories are required by Atelier. The creation of these two directories is up to the user. The project components can be "scattered through" the file system, their access path and names are stored in a file located in the PDB and called project_name.db. In order to create a project from the GUI, you have to click on the AtelierB -> New Project menu, or use either the shortcut Ctrl+P, either a right click on the given workspace, then the New -> Project menu. The project creation wizard will then appear. You will have to choose between B-Software and Event-B. After having typed a project name, the interface will choose directories suitable for the project location, but it will be customizable on the second

7 page of the wizard: You can use the Browse buttons to facilitate the choice of these directories. Once the configuration is done and the wizard closed, the newly created project should appear into the workspace view, and be automatically opened, as shown in the screenshot below: 2. Open this project To open a project into the interface, you have to, click on the Project -> Open menu, or to rightclick on the given workspace on the wanted project, then click on Open. 3. Add components to this project A B project is made up of a list of B components located in text files. These components are either directly linked to the project, or accessible through libraries. The B source files are text files containing one or several components. Once a source file has been attached to a project, the user analyses which components are contained in the file and permit the management of these components. Atelier B only accepts as B source files those whose name ends in one of the four following sufixes :.mch,.ref,.imp,.mod. The contents of each type of file are as follows: A file named Ident.mch must contain one and only one component : an abstract machine named Ident. A file named Ident.ref must contain one and only one component : a refinement named Ident. A file named Ident.imp must contain one and only one component : an implementation named Ident. A file named Ident.mod must contain a component named Ident. It can also contain the refinements of this component, as well as modules (an abstract machine and all its refinements) imported by the implantation of the component. Finally, for each module present in the file, the modules imported by this module can also be present. A sufix file.mod permits the storage in a single file of a B module, or a sub-part of the project made up of a module and the modules imported by this module. If the contents of the files do not respect these rules, the file will still be attached to the project. An error message is then displayed in the startup window. No other operation will be possible on the component before its correction. The GUI is launched, and a project is opened. In order to add components from existing files, you can use the Project -> Add Components. This will lead you to a file selection dialog. Note that the file selection can be multiple if you have to add more than one file. Once the desired files are selected,

8 confirm by clicking on the _Open_ button. Another solution will be to create a new component, if it does not exist. To do so, select in the contextual menu New -> Components.._, or click in the blue + icon onto the toolbar. It will then display the following wizard : Once the name of the new component, the component type, the potential raffined component and the destination path are entered, click on the Next button. Once those steps accomplished, you can begin to apply B Method on your components; the Atelier B allows you to: 1. Perform the syntax analysis and the Type Check This function combines the syntax analysis and the type checking of B components. The syntax checking ensures that the sources for the selected machines comply with the B language syntax. Type checking controls: identifier confiicts, typing rules, missing declarations, language restrictions, visibility rules, etc... This type check is necessary for the PO generation. The type check of a component is automatically applied to all the components required by the current component, through the following links SEES, USES, INCLUDES, IMPORT, EXTENDS, REFINES. This type check on the required components is only applied when necessary, i.e. if a component change was made since the last type check

9 .Modifications of _form_ (comments, spaces,...) are not taken in account. Syntax errors are displayed in an error window and in the start-up window. They are displayed as following: <file>:<line number>:<column number> <error description> Example: AA.mch:6:17 Sequential (';') substitution is not allowed in a specification Line and column numbers show exactly the location in the source file where the error occurs. Semantic errors are displayed in the Atelier B start-up window. They are displayed as following: Type checking machine AA Loading referencedfimachines Checking nameficonflicts Checking constraints clause... Checking INVARIANT clause Error: 1+2 in ( aa: 1+2 ) should be a set Error: Variable aa has not been typed Checking operation b_ask_code Checking operation b_code_typed No information saved for AA End of Type checking The type checker displays an information message for each processed clause. The GUI is launched and a project is opened. To do a syntax analysis and a type check on components, you have to: 1. Select the desired components into the components list, 2. Click on the _Typecheck_ button. Each component is processed successively. If there is a syntax error, an error window will be displayed. This window contains the description of the detected errors. If there is a semantic error on one of the components, a warning window will be displayed. In this case, check the type of error according to the messages displayed in the start-up window. If a syntax error occurs, the error is reported with a description into the errors view. 2. Generate the Proof Obligations This function produces the proof obligations of a component. The component must be type checked. The proof obligations are defined by the B method. They depend on the level of the software development: In machines, the selected mathematical model must be consistent. In the following steps, you must prove that refinements keep the properties of the previous step model. These obligations can be large and complex formulas. The Proof Obligations Generator function split the theoretical PO into many simpler PO. Some PO is so easy to prove that the PO Generator can prove them by itself. In return, the initially foreseen number of formula increases. Some PO defined as obvious are automatically eliminated by the tool. Before generating the proof obligations for a component, Atelier B ensures that the component is type checked. Otherwise, the type check is automatically performed. Generating proof obligations creates four files in the PDB: the comp_name.po file contains the PO of the comp_name component. the comp_name.opo file contains the obvious PO of the comp_name component. the comp_name.pmi file contains the status of the proof obligations (proved/not proved) as well as the interactive demonstrations. the comp_name.stc file contains a description of the component.

10 3. Automatically demonstrate some of these Proof Obligations To launch the automatic prover on some components, you have to perform the following instructions: Select the components into the list, Click on the _Component -> Proof _ menu, and on the desired force. This function automates, in the limit of its ability, the demonstration of the proof obligations for each B component. The messages of the automatic prover are displayed in the start-up window as shown below: Proving B_Delays Proof pass 0, still 3 unproved PO clause b_init_delas -+ End of Proof Initialisation Proved 0 Unproved 0 b_init_delay Proved 1 Unproved 0 b_stop_delay Proved 0 Unproved 0 b_delay_is_up Proved 3 Unproved 0 TOTAL for B_Delays Proved 4 Unproved 0 4. Displaying the Proof Obligations and Use the interactive prover to demonstrate remaining proof obligations This tool enables: displaying the proof obligations of a component clause by clause, displaying obvious proof obligations, i.e. those that were eliminated by the proof obligations generator, Displaying and printing proof obligations using mathematical fonts via a word processing program. The proof obligations include comments that specify: the origin of the assumptions (for example: Component invariant), The theoretical justification of the proof obligation. Click on the given component, and trigger the _Component -> Proof -> Interactive Proof..._ menu.

11 IMPORTANT DATES TO REMEMBER Project Proposal: Submission Date: 19 th April,2013 before 10:00 am Format: Project Name. Members (maximum 3 members). Project requirements. Progress Report: Submission date: 3 rd May, Final project submission: From 20 th May 2013 to 24 th May 2013 For any Queries: saima.zareeen@uettaxila.edu.pk saima_nazir_91@yahoo.com